Phase shift frequency dividers



Aug. 20, 1968 f G, OLSQN 3,398,378

PHASE SHIFT FREQUENCY DIVIDERS original Filed April s, 1965 osclLLA-nouKEYnNC aAmlFYmcf GmNaRA'rom Gilzurr on oRcAvA FUNDA E TA 80 M N L.l

FUNDAMENTAL 5m: wAve NveNTol @Hl/l0 6- 04.50A/

United States Patent O 3,398,378 PHASE SHIFT FREQUENCY DIVIDERS David G.Olson, W. 219 S. 7216 Crowbar Drive, Muskego, Wis. 53150 Continuation ofapplication Ser. No. 445,537, Apr. 5, 1965. This application Feb. 7,1968, Ser. No. 703,794 4 Claims. (Cl. 331-76) ABSTRACT F THE DISCLOSUREA device for dividing the frequency of an AC signal, utilizing a singleamplifying device, and employing phase-cancellation to eliminate everynth input signal pulse, such phase-cancellation occurring by taking fromthe amplifying device, a signal which has zero phase difference relativeto the input signal, shifting it in phase by means of a phase-shiftnetwork, and applying the shifted signal back to the input where it mayat least partially cancel out every nth input pulse `due to thephase-difference between the input and the shifted signal fed back, andpermitting control over the output of the amplifying device, which is180 electrical degrees different, in terms 0f wave shaping Withoutaffecting the ability of the device to divide the frequency.

This is a continuation of application Ser. No. 445,537, filed Apr. 5,1965.

This invention relates to frequency dividers of ele-ctrical oscillationsin general, and more particularly to electrical frequency dividersadapted for use in electri-cal musical instruments.

Frequency division in electrical musical instruments is employed toproduce required frequencies without need for more than a fewoscillators. This is desirable since a frequency divider is normallymore economical to construct, and because it requires no tuning, beinglocked into an exact mathematical relationship 'with its source ofdriving signals. Generally, frequency dividers 'are required to dividethe driving signal by two, producing a note one musical octave lower,but may be made to divide in theory by almost any number. Many types ofdivider circuits require the use of two thermionic tubes orsemi-conductors which makes them less economical than a divider whichrequires but one such device. In addition, many dividers produce only asingle type of output wave and are not capable of being modified invarious ways to produce different types of wave shapes or tone as mightbe required.

It is, therefore, an object of this invention to provide an improvedfrequency divider which requires but a single thermionic tube orsemi-conductor amplifier.

It is vanother object of this invention to provide an improved frequencydivider which will produce several different wave shapes simultaneously.

It is another object of this invention to provide an improved frequencydivider which may be easily modified to produce still further waveshapes by the addition or modification of components, independent of itsoperation.

Another object of this invention is to provide an irnproved frequencydivider which will operate over a relatively wide range of frequenciesso that its operation is not impaired by the driving signal varying fromthe' original frequency.

Still another object of this invention is to provide an improvedfrequency divider which will operate in la satisfactory manner eventhough there are variations in supply voltage to the thermionic tube orsemi-conductor.

"ice

Other and further objects of this invention will become 'apparent as thefollowing description proceeds, reference being had to the accompanyingdrawings, in which:

FIGURE 1 is a schematic of the circuit of an embodiment of thisinvention employing a semi-conductor amplier.

FIGURE 2 is a schematic of the circuit of an embodirnent of thisinvention employing a thermionic tube amplifier.

FIGURE 3 is another embodiment of the invention employing asemi-conductor device and having tone shaping elements added.

FIGURE 4 is an illustration of some of the various waveforms obtainablefrom the circuits.

FIGURE 5 is an illustration of the relationship of the fundamentalsinewaves and their effect on the Waveform at the base of thesemi-condu-ctor.

In an amplifying circuit, signals appearing at the input are reproducedat the output, generally in amplified form. In the use of an amplifyingdevice for frequency division, it is necessary that only every nthsignal to the input be present at the output, and the uniquecharacteristics of the amplifying device are employed to prevent theunwanted input pulses from reaching the output. Where every secondsignal is obtained at the output, the divider is dividing by two, whilewhere every fourth signal is present, it is dividing by four. While thedescription here is confined to such action occurring in a semiconductordevice, it is equally applicable to a thermionic tube as well. In thispatent, the phase relationship between emitter and base is used tocontrol the frequency division, and `determines the signal reaching thecollector. This permits modifications of the collector circuit toproduce varying types of waveforms without affecting the operation ofthe divider while in the convention divider, the collector is anintegral part of the circuit so that modification of collector circuitswill cause the divider to operate unsatisfactorily or requireconsiderable revision to component values in other parts of the circuit.Adjustment of the strength of the driving signal will also have aneffect on the output waveforms. Thus, -while a change in driving signalstrength will affect the tone quality to some extent, the divider willcontinue to produce the correct frequency over a relatively wide rangeof variation in input signal strength. Likewise, a change in supplyvoltage will alter the amplification characteristics of thesemi-conductor and produce the same effect as altering the strength ofthe input signal, making it possible for the divider to operatesatisfactorily over a relatively wide range of supply voltages as wouldbe encountered .in a commercial electronic musical instrument where ahigh degree of voltage regulation is not practical.

Referring to FIGURE l, a semi-conductor 14 is shown in a common emitterconfiguration. A battery 18 supplies current to the collector 15 throughresistor 19 and a bias current to base 17 through resistors 20 and 21act as a voltage divider. An oscillation generator 10 supplies a drivingsignal to the base 17 through resistor 13, but this signal may besupplied by another divider as well. The output of the divider is takenfrom the collector 15 through capacitor 25 where it is shown going tothe keying and amplifying circuit of an organ. This output may be usedto drive another divider also. Resistor 22, capacitors 23 and 24, andresistor 21 form a phase-shift or time constant network between theemitter .16, base 17, and ground 12. Capacitor 24 also constitutes afeedback path between emitter 16 and base 17. Normally, if a conductingpath having little or no phase-shift or time delay were connectedbetween the collector-emitter circuit and the base-emitter circuit, aloss in overall gain would be the only result. If, however, this pathtakes the form of an integrating phase-shift network,'two effects areobtamed. In the first place, the integrating characteristics of thefeedback path attenuate the higher frequency components present in thecollector-emitter waveform. Second, the phase-shift characteristics ofthe feedback path ret1red the phase of the residual sinewavefundamental. It will be found that said fundamental component at theemitter lags by approximately 9() degrees, the semi-conductor currentoccasioned by the input signal peak. This is caused by the non-linearoperating characteristics of the semi-conductor in conjunction with acapacitive baseemitter circuit. The resultant composite waveform nowpresent at the base-emitter circuit is of such conguration as to causecollector current flow at periods equal to a sub-multiple of the periodof applied signal. The phaseshift network can be designed to cause aphase-shift approaching 90 degrees without excessive attenuation. Thisphase-shift is dependent, for the most part, on the time constants ofthe two RC portions of the phase-shift network, namely, resistor 22 withcapacitor 23, and resistor 21 with capacitors 23 and 24 in series. Whena signal is applied to the base 17 through resistor 13 from source 11,the first negative pulse will be amplied by semiconductor 14 and appearat the collector 15. Due to the conduction of semi-conductor 14, asimilar waveform will appear at emitter 16 Ibut opposite in phase to thecollector waveform 180 degrees different. The doublephase shiftingnetwork consisting of resistor 22 and capacitor 23, and secondly, ofresistor 2.1 and capacitors 23 and 24 combine to produce the followingeffect: due to the integrating characteristics of these networks, thefeedback path through capacitor 23 attenuates the high frequencycomponents present in the emitter circuit waveform and, therefore, doesnot feed these components back to the base 17. The phase-shiftingcharacteristics of this feedback path are such as to retard the phase ofthe residual sinewave fundamental fed back from the emitter 16 circuitto the base 17. However, because the source of feedback signal is in thebase-emitter circuit rather than external to it, both the sinewavefundamental and the phase-shifted sinewave fundamental appear at thebase 17 of the semi-conductor 14. This results in the reduction inamplitude of both positive and negative peaks of the second input pulseas can be seen in FIGURE 5.

FIGURE illustrates frequency division by two, in which every secondinput pulse is attenuated by phase cancellation. The fundamental inputsignal is represented by waveform 80. The phase shifted signal feedbackemitter 16 is represented by Waveform 81. For purposes of illustration,waveform 81 is shown as lagging waveform 80 by 90 degrees. The resultantwaveform imposed on the semiconductor base 17 is represented by waveform82, in which every second peak is attenuated. The net effect of thisfeedback path is that during the time when the second input pulse fromthe oscillator is applied to the base 17 through resistor 13, thesemiconductor is held almost completely below cutoff and, therefore, theinput pulse does not appear in the collector output in any substantialamount. The phase of the shifted fundamental sinewave will lag the phaseVof the fundamental sinewave by 90 degrees. It should be noted thatsince there is no 180 degree phase inversion between the input signaland the fundamental sinewave at the emitter 16, it is the fundamentalsinewave that actually holds the sem-conductor below cut off on everyother input pulse and not the phase-shifted fundamental sinewave. Whileresistor 21 and capacitor 24 are essential to the operation of thisdivider, a slightly different view of this network will show thatresistor 21, and capacitors 23 and 24 cornprise an RC network with atime constant equal to the period of input waveform. It is this factthat accounts for the successful operation and stability of thisdivider. Without the parallel RC network for the fundamental sinewave atthe emitter to modify, operation of this divider would not be possible.

In FIGURE 2, the comparable circuit is' shown employing a thermionictube 34, having a plate 35, a grid 37, and a cathode 36. A source ofvoltage, a battery 44 supplies voltage to the plate 35 throughy resistor45. Driving signal is supplied to the grid 37 through resistor 33 fromsource 31. Phase-shift network is comprised of resistors 38, 39 and 4t),and capacitors 41 and 42. Resistor 40 is not essential to the operation,but may be added to obtain an additional waveform at point 46 withoutaffecting the operation of the divider. Output is obtained from theplate 35 through capacitor 43. The principle of operation is similarwith cutoff occurring at the grid of the tube.

FIGURE 3 illustrates another version of the divider where capacitor 61and resistor 63 are connected in series to produce a different waveformat the collector 53 of semi-conductor 50. An additional waveform may beobtained at point 64, or the circuit may be operated Without resistor63. Varying the values of both resistor 63 and capacitor 61 will producevarious waveforms at the co1- lector 53. The effect of these additionalcomponents on the operation of the divider is limited to their effect onthe waveshape obtained at the col-lector 53.

FIGURE 4 illustrates the various waveforms which may be obtained fromthe divider operating under various conditions. Waveform 70 is obtainedfrom the collector of the semi-conductor in FIGURE l or the plate of thetube in FIGURE 2. The slight pulse 71 may be increased in size oreliminated by varying the value of resistor 13 in FIGURE l or resistor33 in FIGURE 2 which alters the strength of the driving signal. Waveform72 is obtained from the collector at point in FIG. 3 while waveform 73is obtainable from point 64 in FIG. 3. Waveform 74 is obtained frompoint 65 in FIG. 3 when the strength of the driving signal is increasedby lowering the value of the resistor 56 in FIG. 3 and waveform 75 isobtained from point 64 in FIG. 3 under the same conditions. Waveform 76is obtained from the emitter 16 in FIG. l. Other waveforms may beobtained from the emitter 54 in FIG. 3.

What is claimed and desired to be secured by Letters Patent of theUnited States, is:

1. An apparatus for dividing the frequency supplied by a source ofelectrical oscillations having a predetermined frequency, said apparatuscomprising a semi-conductor device having a base, an emitter, and acollector, said base comprising the input circuit connected to saidsource of electrical oscillations, a phase-shift network connectedbetween the base and emitter of said semiconductor, said phase-shiftnetwork producing a phaseshift of the electrical oscillations fed backfrom the emitter to the base of said semi-conductor such that phasecancellation externally of the semi-conductor attenuates every nth inputpulse of said electrical oscillations received at the input andproducing a frequency at the collector of said semi-conductor equal tothe input frequency divided by n.

2. The apparatus of claim 1 in combination with a wave shaping networkconnected with the collector of the semi-conductor device, fordetermining the harmonic content of the output frequency.

3. An apparatus for dividing the frequency supplied by a source ofelectrical oscillations having a predetermined frequency, said apparatuscomprising a thermionic tube having a grid, a cathode and a plate, saidgrid comprising the input circuit connected to said source of electricaloscillations, a phase-shift network connected between the grid andcathode of said tubehsaid phase-shift network producing a phase-shift ofthe electrical oscillations fed back from the cathode to the grid ofsaid tube such that phase cancellation externally of the tube attenuatesevery References Cited nth input pulse of said electrical oscillationsreceived UNITED STATES PATENTS at the mput and -produclng a frequency atthe plate of said tube equal t-o the input frequency divided by n.2126682 8/1938 Hammond 331-51 X 4. The apparatus of claim 3 incombination with a 5 2,665,379 1/1954 Hadden 331-51 wave shaping networkconnected with the plate of said I l f' tube for determining theharmonic content of the output ROY LAKE Pr'ma'y Exammer frequency. J. B.MULLINS, Assistant Examiner.

